General Chemistry Chapters 19, 21, 22

HOMEWORK EXAM 3:

Chapter 19:

The half life of 90Sr is 29 years. What fraction of the atoms in a sample of 90Sr would remain 175 years later?
Answer

0.166

0.125

0.062

here
0.015

Which relation is not correct?
Answer

11p = 11H = proton

0-1e = 0-1β = electron

here
+10e = +10β= positron

10n = neutron

As a result of beta decay, the product nucleus is
Answer

one atomic number lower than the original element.

two atomic number higher than the original element.

here one atomic number higher than the original element.

two atomic number lower than the original element.
What is X for the nuclear reaction: 21284Po à 20882Pb + X
Answer

42p

1-1β

here
42α

11n

Which statement is not correct for the nuclear reaction: 146C à 147N + 0-1β ?
Answer

C is radioactive.

Nucleus of C is not stable.

Here?
N lies above the belt of stability of nucleus.

One neutron in the nucleus of C converts to a proton with the release of the release of particle.

If 12% of a certain radioactive isotope decays in 5.2 years, what is the half-life of this isotope?
Answer

0.59 yr

1.7 yr

21.7 yr

here
28.1 yr

Which statement is false?
Answer

No chemical treatments can make radioactive elements harmless.

The rate of decay (disintegration) of U-238 is proportional to its sample size.

Changes in temperature or pressure cannot affect the rate of decay (disintegration) of radioactive elements.

F
Decay constant maintains its constancy only at the specific temperature.

How much energy is lost or gained when a mole of cobalt-60 undergoes beta decay:
6027Co --> 6028Ni + 0-1e ?
The mass of the 6027Co atom is 59.933819 amu, and that of a 6028Ni atom is 59.930788 amu.
Answer

Here?
2.724x1011 J energy is released.

2.724x1011 J energy is absorbed.

2.724x108 J energy is released.